1. Field of the Invention
The invention relates to a transmission device, more particularly to a transmission device capable of preventing reverse transmission.
2. Description of the Related Art
FIGS. 1 and 2 illustrate a conventional electric parking brake mechanism 13 disclosed in U.S. Pat. No. 6,938,736. The conventional electric parking brake mechanism 13 is characterized by an electric parking brake for pressing a friction member to a braked member via a force transmission converting mechanism 10 for converting a rotational movement of the motor 11 to a linear movement. The conventional electric parking brake mechanism 13 includes an input shaft 130, an output shaft 122, a non-rotating member 131, a rotating member 132, a first cam member 135, two second cam members 134, a spring 137 and two balls 136.
In such a configuration, the first and second cam members 135, 134 are used, thereby resulting in relatively high cost. Furthermore, when the motor 11 is operated in high-speed rotation, friction between the balls 136 and the non-rotating member 131 occurs due to a centrifugal force acted on each ball 136, thereby reducing efficiency. Moreover, due to friction between the balls 136 and the non-rotating member 131, wear of the balls 136 and the non-rotating member 131 occurs, thereby increasing a clearance between each ball 136 and the non-rotating member 131. Therefore, accurate operation cannot be ensured after a long period of use.